1. Field of the Invention
This invention relates to a method for dyeing cellulose fibers using a disperse dye.
2. Description of the Prior Art
In general, the disperse dye has an excellent color affinity to synthetic fibers, especially to polyester fibers, but has poor color affinity to the cellulose fibers. Thus, it is not possible to dye with the disperse dye a product such as a mixed yarn or union cloth of the cellulose and synthetic fibers. Such a product can be dyed by a process in which the disperse dye is used in combination with the use of a direct dye, reactive dye, soluble vat dye, or vat dye; the synthetic fiber portions are at first dyed by the disperse dyes, then the cellulose fiber portions are dyed by said direct dyes, reactive dyes, soluble vat dyes or vat dye. The process, however, has disadvantages because the process is intricate, time-consuming and gives a product with poor color fastness.
The above-mentioned product can be dyed further by a pigment dyeing process and by a process wherein Dyblen (registered trademark) dyes are used. The pigment dyeing process has the advantages that simultaneous printing can be carried out and operations are simple, but has disadvantages that it gives a product having poor color fastness to rubbing and having a rough, coarse tactility. Said Dyblen dyeing process has advantages that simultaneous printing can also be carried out, but has disadvantages in that it gives a product having poor color fastness and having a low resistance to organic solvents. Thus, none of the conventional processes could furnish good dye fastness to a product having the form of mixed yarns or union cloth of cellulose fibers and polyester synthetic fibers. Therefore, those skilled in the art have sought a process which can give color fastness to a product which is composed of mixed yarns or union cloth of cellulose fibers, polyester synthetic fibers. The inventors have invented a process wherein the product can be dyed by the disperse dyes with good color fastness.
It is known that the cellulose fibers are turned into fibers which have a good affinity to the disperse dyes and can be dyed by the disperse dyes when the cellulose fibers are either esterified or etherified. However, the thus esterified or etherified product did not have practical use, because the product loses soft tactility to become stiff and does not show good color fastness. For example, a method is known in which the cellulose fibers are acylated by fatty acid such as acetic acid, propionic acid and butyric acid to improve color affinity of the cellulose fibers, and then the resulting product is dyed with the disperse dyes; however, the product does not show good color fastness, especially color fastness to washing, though the product is more or less improved in color affinity. In order to improve further the color fastness, the cellulose fibers must be more highly acylated by the fatty acid, or a fixing agent must be further used; however, if so, the resulting product is of no practical use owing to inferior tactility.
The inventors intended to obtain cellulose fiber derivatives which could be easily dyed by the disperse dyes, and tried various chemical treatments for improving color fastness of the cellulose fibers. Particularly, the inventors tried to esterify the cellulose fibers by various acids or acid derivatives, for example, benzoic acid, and also to etherify the cellulose fibers, for example, by acrylonitrile. As a result, the inventors have found that the cellulose fibers can be converted into a product, without deteriorating both the tactility and hygroscopic property of the cellulose fibers, which product can be dyed by the disperse dyes clearly and with good color fastness, if the cellulose fibers are appropriately acylated by an aromatic acid such as benzoic acid, and when a substitution degree of acyl group is maintained at an appropriate value. These findings comprise the invention.